/Engine/Source/Runtime/MessagingCommon/Public/MessageEndpointBuilder.h
WithCatchall
[FMessageEndpointBuilder](API\Runtime\MessagingCommon\FMessageEndpointBuilder) & WithHandler ( const [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [IMessageHandler](API\Runtime\Messaging\IMessageHandler), ESPMode::ThreadSafe > & Handler )